Added check for whether the destination user exists

main.c

@@ -20,6 +20,8 @@
 User** create_user_list(char* filename);
 void sigint_handler(int dummy);
 User* fetch_user(char* username);
+int user_to_index(User* user);
+bool user_equals(User* this, User* other);
 
 User** users;
 int num_users;
@@ -120,10 +122,17 @@ int main() {
 					}	
 
 					printf("Your message is: %s\n",message_string);
-					Message message = new_message(message_string,from_user[i],to_user[i]);
 
+					if (user_to_index(to_user[i]) < 0) {
+						printf("Recipient user does not exist!\n");
+						return -20;
+					}
+
+					Message* message = new_message(message_string,from_user[i],to_user[i]);
 					stack_push( message_stack[user_to_index(to_user[i])],message );
 
+					printf("Message has been pushed onto stack for %s\n",to_user[i]->username);
+
 					
 
 					close(conn_sockets[i]);					
@@ -205,7 +214,7 @@ User* fetch_user(char* username) {
 }
 
 int user_to_index(User* user) {
-	int index = 0;
+	int index = -1;
 	for (int i=0;i < num_users; i++) {
 		if (user_equals(users[i],user) == true) {
 			index = i;